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UNIVERSITY  OF  ILLINOIS 


Agricultural  Experiment  Station 


BULLETIN  NO.  154 


WHAT  IS  THE  MATTER  WITH  THE 
ELMS  IN  ILLINOIS? 


By  STEPHEN  A.  FORBES 
STATE  ENTOMOLOGIST 


URBANA,  ILLINOIS,  FEBRUARY,  1912 


SUMMARY  oi-A  BULLETIN  No.  154 

1.  Elms  dying  thruout  many  towns  of  southern  Illinois,  sometimes  slowly 
and  sometimes  suddenly,  the  leaves  turning  brown  and  falling  in  summer,  and 
the  roots  drying  up.  Pages  1-4. 

2.  A  typical  case  described.  Page  4. 

3.  Disease  observed  in   fourteen  towns  scattered  thru  thirteen  counties  of 
southern  and  western   Illinois.     Trees  not  affected  if  under  natural  woodland 
conditions.  Page  5. 

4.  Description  of  same  disease  in  Kentucky.  Pages  5  and  6. 

5.  Similar  disease  in  central  Illinois  in  1883.  Page  6. 

6.  Injury  caused  in  part  by  drouth   and  unnatural  conditions  of  tree,   re- 
sulting  in   starvation ;     in   part  by   borers   in   the   trunk,   attracted   by  unthrifty 
state.     Former  perhaps  the  primary  trouble  in  most  cases.  Pages  7-10. 

7.  Free   watering,    fertilizing,   and   mulching  of  soil  necessary,   at  least  in 
severe  drouth.     Care  required  in  trimming  trees  and  painting  cut  surfaces,  to 
prevent  infestation.     Use  of  various  mixtures  suggested  as  repellents  to  borers. 

Pages  II  and  12. 

8.  Descriptions,  figures,  and  life  histories  of  the  elm-borer  and  the  reddish 
elm  snout-beetle.  Pages  12-16 


WHAT  IS  THE  MATTER  WITH  THE  ELMS 
IN  ILLINOIS? 

BY  STEPHEN  A.  FORBES,  STATE  ENTOMOLOGIST 
(Plates  I  to  VI,  and  Figures  1  to  4) 

The  American  white  elm  is  doubtless  the  favorite  shade  tree 
thruout  Illinois.  It  is  especially  valued  for  its  broad  and  ample 
shade,  its  fairly  rapid  growth,  its  usual  freedom  from  offensive  in- 
sects, and  its  stout  resistance  to  injury  by  wind  storms  and  sleet; 
and  it  is  universally  admired,  also,  for  its  majestic  yet  graceful 
form,  its  picturesque  profile,  and  the  irregular,  cloudlike  masses 
of  its  foliage.  It  is  particularly  well  adapted  to  streets,  boule- 
vards, and  park  drives ;  and  an  avenue  of  giant  elms  whose  lateral 
branches  arch  broadly  upwards  to  meet  and  mingle  overhead  is 
one  of  the  noblest  products  of  the  landscape  gardener's  art. 

I  especially  regret,  therefore,  to  have  to  call  general  attention 
to  a  fatal  affection  of  this  tree  now  prevailing  over  a  large  part  of 
southern  Illinois,  similar  to,  and  apparently  identical  with,  one 
which  destroyed  many  elms  in  the  central  part  of  the  state  some 
thirty  years  ago.  The  character,  extent,  and  cause  of  this  destruc- 
tion are  such  as  to  make  it  plain  either  that  the  elm  must  receive 
much  more  intelligent  and  assiduous  care  and  treatment  than  it  has 
heretofore  had  in  this  state,  or  that  it  must  yield  its  place  to  some 
tree  more  hardy  under  conditions  which  it  has  itself  failed  to  sup- 
port. 

DESCRIPTION  OF  THE  DIFFICULTY 

The  elm  disease  (if  such  it  may  be  called)  now  prevalent,  is 
first  noticed  from  early  summer  to  autumn — the  leaves,  first  on 
the  terminal  twigs  and  later  on  the  larger  branches,  ceasing  their 
growth,  turning  brown,  and  finally  falling.  (See  Plates  I  to  IV.) 
This  loss  is  presently  followed  by  the  death  of  the  branches  them- 
selves, as  is  shown  the  following  spring  when  the  rest  of  the  tree 
leaves  out.  Usually  the  higher  branches  are  first  affected,  but  the 
whole  top  soon  seems  to  blight,  and  in  a  year  or  two  the  tree  is 
dead.  Sometimes  this  process  is  greatly  shortened,  and  scores  of 


4  BULLETIN  No.  154  [February. 

trees  may  perish  within  a  single  year  after  the  first  effects  are  no- 
ticed; and  sometimes,  on  the  other  hand,  it  is  greatly  lengthened, 
extending  thru  five  or  six  years,  and,  in  mild  cases,  even  ending  in 
recovery.  Altho  there  may  be  no  definite  sign  of  insect  injury 
anywhere,  it  is  most  commonly  the  case  that  a  thoro  search  of  the 
trunk  and  larger  branches  will  show  patches  of  dead  bark  under 
which  there  are  two  or  more  kinds  of  burrowing  insect  larvae,  or 
borers.  The  roots  of  these  trees  are  often  affected  somewhat  as 
the  branches  are;  that  is,  the  smaller,  terminal,  so-called  feeding 
roots  die  and  dry  up  progressively,  the  process  extending  to  the 
larger  roots  and  the  base  of  the  trunk. 

A  TYPICAL  CASE 

The  condition  of  the  roots  of  trees  so  affected  is  well  shown  by 
the  report  of  Mr.  Lindley  M.  Smith,  my  field  assistant  for  south- 
ern Illinois,  who  visited  Du  Quoin,  Perry  county,  in  July  of  the 
current  year  for  an  examination  of  elms  reported  to  be  dead  or 
dying.  This  visit  was  in  pursuance  of  a  letter  addressed  to  me 
by  Mr.  E.  E.  Jacobs,  mayor  of  the  town,  who  says,  under  date  of 
July  8 :  "At  the  time  the  city  of  Du  Quoin  was  laid  out,  some  fifty 
years  ago,  our  streets  were  lined  with  elm  trees.  These  trees  have 
gotten  along  nicely  up  to  the  present  summer,  but  now  there  are 
probably  a  hundred  and  fifty  trees  dead  or  dying."  Mr.  Smith 
reports,  July  14:  "The  elms  are  in  very  bad  condition,  and  there 
are  many  dead  or  dying  ones  all  over  town.  The  round-headed 
borers  [Fig.  i]  are  very  thick  under  the  bark  on  these  dying  trees, 
and  the  people  in  general  seem  to  suppose  that  the  borers  are  the 
cause  of  all  of  the  damage.  I  dug  out  some  of  the  main  roots  on 
seven  large  trees,  and  while  many  of  the  roots  were  still  green  for 
a  few  feet  from  the  base,  I  invariably  found  that  the  little  feeding 
roots  were  dead.  In  some  cases  the  smaller  roots  had  apparently 
been  dead  for  several  days,  or  perhaps  weeks,  as  they  were  all  dis- 
colored and  some  were  almost  rotten.  We  dug  one  tree  out  so  that 
all  of  the  roots  could  be  examined.  The  outer  ends  of  all  the  roots 
on  this  tree  were  dead,  tho  some  of  the  main  roots  \vere  still  alive, 
and  the  leaves  were  not  yet  quite  all  dead.  The  tree  had  no  tap- 
root, all  the  roots  spread  out  from  the  base  of  the  tree,  and  none 
of  them  were  very  far  beneath  the  surface.  I  found  no  sign  of  in- 
sect work  on  the  roots,  but  most  of  the  latter  simply  looked  as  if 
they  had  dried  up.  The  ground  was  very  dry,  as  there  has  been 
no  rain  that  would  wet  down  to  the  tree  roots  since  some  time  in 
April."  Similar  conditions  were  found  by  Mr.  Smith  at  Carbon- 
dale,  where  one  tree  was  dug  up,  together  with  a  number  of  roots 


1912]  WHAT  is  THE  MATTER  WITH  THE  ELMS?  5 

of  other  trees,  on  the  campus  of  the  Normal  School ;  all  the  small 
feeding  roots  of  these  trees  were  dead,  altho  there  was  nothing 
about  them  to  indicate  injury  by  insects. 

DISTRIBUTION  OF  THE  INJURY 

Practically  identical  reports  of  injury  have  been  received  this 
year,  either  from  my  own  assistants  or  from  office  correspondents., 
from  Cairo,  Carbondale,  Centralia,  Clayton,  Du  Quoin,  Edwards- 
ville,  Fairfield,  Galatia,  McLeansboro,  Mt.  Vernon,  Quincy,  Rob- 
inson, Sumner,  and  Vandalia — fourteen  towns  scattered  thru  thir- 
teen counties  of  southern  and  western  Illinois.  Doubtless  a  criti- 
cal examination  of  elm  trees  in  towns  and  on  private  premises 
elsewhere  would  disclose  an  even  more  general  occurrence  of  this 
trouble. 

As  none  of  the  cases  reported  were  from  woodlands,  but  all 
were  those  of  more  or  less  isolated  trees  growing  under  artificial 
conditions,  I  have  taken  some  pains  to  ascertain  whether  woodland 
elms  were  similarly  affected.  One  of  my  assistants,  Mr.  Wesley 
P.  Flint,  made  in  1909-10  a  practically  complete  reconnaissance  of 
all  the  forests  of  southern  and  western  Illinois,  including  high 
lands  and  bottom  lands,  hills  and  plains,  and  the  extremes  of  the 
state  from  Jo  Daviess  to  Alexander  counties.  His  object  was  to 
make  a  comprehensive  study  of  insect  injuries  to  forest  trees  and 
timber  products  in  this  state.  In  reply  to  my  special  inquiry  he 
says :  "I  have  not  found  elms  dying  in  any  numbers  in  any  forest 
tract  that  I  have  examined  in  the  state.  This,  of  course,  does  not 
apply  to  stands  of  scattered  trees  around  which  the  ground  has 
been  cultivated."  Mr.  Smith,  who  was  especially  instructed  to  in- 
spect woodland  trees  about  Du  Quoin  for  a  comparison  of  their 
condition  with  those  in  that  town  itself,  reports  that  he  saw  a  hun- 
dred and  fifty  elms  in  the  \voodlands  along  Reese  Creek  and  Little 
Muddy  Creek  bottoms,  but  found  none  that  were  dying,  and  none 
that  had  died  during  the  present  summer,  altho  a  few  had  perished 
from  some  cause  at  some  time  within  the  last  three  years. 

The  present  difficulty  with  the  elm  in  the  southern  part  of  the 
.state  is  thus  clearly  one  which  is  virtually  limited  to  trees  growing 
outside  the  forests,  and  usually  under  conditions  more  or  less  artifi- 
cial to  the  tree — sometimes  extremely  so,  where,  for  example,  the 
elms  are  standing  in  a  closely  clipped  turf  beside  a  paved  street. 

A  KENTUCKY  INSTANCE 

All  the  facts  in  my  possession  indicate  that  our  Illinois  elm 
disease  is  identical  with  one  described  in  1899  by  Professor  H. 


6  BULLETIN  No.  154  [February, 

Carman,  Entomologist  and  Botanist  of  the  Agricultural  Experi- 
ment Station  of  Kentucky.*  "Beginning,"  he  says,  "in  1892,  and 
continuing  with  greater  or  less  frequency  ever  since,  complaints 
have  reached  me  concerning  a  diseased  condition  of  elm  trees  in  this 
State.  *  *  *  Previous  to  1892  there  is  every  probability  that 
the  trouble  was  under  way.  It  was  observed  in  Massachusetts  in 
1847,  ar|d  in  Illinois  in  1883.  *  *  * 

"The  first  discernible  evidence  of  disease  is  a  loss  of  the  leaves 
at  the  ends  of  twigs,  often  at  the  tops  of  the  trees.  As  the  trouble 
extends  towards  the  trunk,  the  foliage  gradually  drops  from  other 
parts  until  finally  the  tree  stands  bare.  [Plates  I  to  IV.]  The 
fallen  leaves  may  show  no  mark  of  insect  work,  certainly  none  that 
could  cause  them  to  let  go  their  hold  on  the  branches,  and  the  only 
thing  abnormal  about  them  is  a  discoloration,  sometimes  present, 
like  that  due  to  the  blight  fungus  of  potatoes,  the  tips  or  side 
regions  being  more  or  less  extensively  black." 

AN  EARLIER  ILLINOIS  CASE 

As  already  intimated,  what  seems  to  have  been  a  similar  trouble 
with  the  elms  prevailed  some  time  since  in  the  central  part  of  this 
state.  It  was  in  1883,  in  fact — the  first  year  of  my  service  as 
State  Entomologist  of  Illinois — that  this  matter  first  came  to  my 
notice ;  and  during  that  and  the  three  following  years  I  studied  the 
diseased  elms  with  considerable  care  at  Normal,  Bloomington,  and 
Champaign,  publishing  a  short  article  on  the  subject  in  my  third 
entomological  report,  f  I  was  aided  in  this  work  by  Professor  Gar- 
man,  who  was  at  that  time  in  my  office;  and  he  has  had,  conse- 
quently, an  opportunity  to  compare  the  Illinois  disease  with  that 
studied  by  him  even  more  thoroly  in  Kentucky. 

THE  PRESENT  SITUATION 

My  attention  was  first  and  most  forcibly  called  to  the  present 
situation  by  a  letter  addressed  to  the  University  of  Illinois  in  1907 
by  Hon.  John  M.  Rapp,  of  Fairfield,  in  Wayne  county,  and  re- 
ferred to  my  office  for  reply.  In  this  letter  he  says :  "We  in  this 
city  are  troubled  with  something  that  is  causing  the  death  of  the 
elm  shade  trees.  The  matter  seems  to  be  growing  worse  each  year. 
Some  of  the  largest  and  finest  trees  have  died,  and  the  trouble  does 
not  seem  to  be  confined  entirely  to  the  oldest  and  largest  trees."  In 


"The  Elms  and  Their  Diseases."     Bull.  84,  Ky.  Agr.  Exper.  Station, 
flnsects  Injurious  to  the  Elm.     14th  Rep.  State  Ent.  111.,  p.  112. 


1912]  WHAT  is  THE  MATTER  WITH  THE  ELMS?  7 

a  later  letter  he  says :  "The  elm  trees,  not  only  in  this  city,  where 
they  have  been  our  chief  shade  tree,  but  in  the  surrounding  coun- 
try, are  dying  from  some  disease  that  is  a  mystery  to  our  people. 
There  is  apparently  no  disease  of  the  leaf — no  web  formed — but 
the  leaves  begin  to  dry  up  and  to  die,  and  finally,  in  a  few  months, 
the  tree  is  dead.  A  number  of  the  finest  shade  trees  in  the  city 
have  gone  that  way.  There  are  many  that  now  show  evidences  of 
the  disease." 

In  consequence  of  this  information  I  sent  to  Fairfield  in  the 
fall  of  1907  Mr.  H.  E.  Hodgkiss,  an  entomological  assistant  in  my 
office  at  the  time.  As  the  primary  cause  of  the  disease  seemed  a 
matter  of  doubt,  and  might  possibly  be  a  fungous  infection,  or 
even  cultural  conditions  merely,  Mr.  Hodgkiss  was  accompanied  on 
his  trip  by  Professor  T.  J.  Rurrill,  of  the  University  of  Illinois, 
who  kindly  consented  to  assist  us  in  the  solution  of  the  problem. 
After  a  thoro  examination  of  several  dead  and  dying  trees  in  and 
about  Fairfield  these  gentlemen  came  to  the  conclusion  that  the 
cause  was  a  complex  one,  but  differed  in  judgment  as  to  the  pri- 
mary factor,  Professor  Burrill  believing  it  to  be  the  round-headed 
borer  of  the  elm  (Saperda  tridentata,  Fig.  i),  which  was  abundant 
under  the  bark  of  most  of  the  injured  trees,  and  Mr.  Hodgkiss 
concluding,  on  the  other  hand,  that  the  original  difficulty  was  in 
the  roots. 


The  condition  of  the  roots  described  above  by  Mr.  Smith  and 
a  general  infestation  of  the  trunk  and  larger  branches  by  borers, 
are  found  together  at  the  same  time  and  place,  and  usually  in  the 
same  trees.  The  well-known  disposition  of  the  borers  generally, 
and  especially  of  the  elm-tree  borer,  to  infest  first  and  most  freely 
trees  already  suffering  from  some  other  cause,  adds  to  our  uncer- 
tainty concerning  the  share  which  these  two  causes  may  take  in  the 
destruction  of  our  elms.  It  is  probable  that  sometimes  one  is  pri- 
mary, and  sometimes  the  other.  The  root  injury  may  come  to  a 
tree  already  infested  by  borers,  or  the  borers  may  come  to  infest  a 
tree  already  affected  at  the  roots,  each  injury  intensifying  the 
other,  and  both  together  destroying  trees  which  might  survive 
either  alone.  Even  elm  trees  in  the  forest  are  more  or  less  infested 
by  the  round-headed  borer  and  other  insects  of  similar  habit.  Mr. 
Flint  reports,  for  example,  that  in  his  inspection  of  woodlands,  he 
found  this  borer  abundant  in  dying  trees  thruout  the  state,  and 
the  larva  of  the  elm  curculio  (Magdalis  armicollis,  Fig.  3,  4)  even 
more  abundant  in  the  northern  counties.  Small  bark-beetles  were 


8  BULLETIN  No.  154  [February, 

also  very  common  in  the  bark  of  both  dead  trees  and  those  other- 
wise healthy. 

The  elm  in  its  natural  habitat  grows  in  a  loose  and  shaded  soil 
composed  of  leaf  mold  to  a  considerable  depth,  and  does  not  root 
deeply.  (See  Plate  VI.)  If  other  trees  and  the  underbrush  which 
afford  more  or  less  protection  to  the  elm  roots  are  cut  away,  and 
especially  if  the  land  is  pastured  and  the  soil  thus  packed,  or  if,  as 
in  the  city,  the  root  system  is  cramped  in  earth  sometimes  perme- 
ated by  escaping  gas,  too  closely  packed,  unmulched,  and  unnatu- 
rally drained,  and  exposed  for  long  summer  periods  to  the  hot 
glare  reflected  from  the  paved  streets,  the  leaves  of  the  tree  in 
the  meantime  being  constantly  exposed  to  gas  and  smoke,  and  cov- 
ered for  weeks  with  dust  from  the  street,  we  have  an  environment 
for  this  tree  as  unnatural  as  it  would  be  possible  to  make  it  and 
permit  the  tree  to  live  at  all.  The  feeding  roots  are  thus  exposed 
to  drouth,  and  sometimes  remain  for  weeks  at  a  time  about  as  dry 
as  the  dust  of  the  street.  The  soil  is  exhausted  of  plant  food,  and 
nothing  is  done  to  renovate  it.  The  tree  is  starved  and  weakened, 
the  uppermost  twigs  begin  to  die,  and  insects,  instinctively  attracted 
to  the  weaker  trees,  come  in  and  finish  the  work.  Their  injury,  at 
first  scarcely  perceptible,  serves  merely  to  accelerate  the  decline  of 
the  tree,  but  sometimes,  unfavorable  conditions  having  reached  a 
temporary  climax,  the  work  of  the  borers,  stimulated  rather  than 
retarded  by  such  conditions,  quickly  overwhelms  the  tree,  girdling 
its  trunk  and  killing  it  as  if  by  a  sudden  stroke. 

Professor  Garman  is  sure  that  in  Kentucky  insects  were  not 
the  primary  cause  of  the  wide-spread  loss  of  elm  trees  in  1899  and 
the  years  preceding.  His  discussion  of  conditions  and  effects  is  so 
instructive  and  convincing  that  I  quote  from  it  at  length. 

"The  white  elm,"  he  says,  "has  a  peculiar  way  of  sending  its 
main  roots  out  close  to  the  surface  of  the  ground.  Sometimes  a 
root  upon  which  a  tree  chiefly  depends  is  covered  in  places  with 
less  than  two  inches  of  soil.  Roots  after  leaving  the  base  of  the 
trunk  actually  turn  toward  the  surface,  where  they  extend  for 
long  distances  in  the  rich  surface  soil.  The  trees  taken  up  on  the 
college  grounds  for  examination  illustrate  the  point  very  well. 
[Plate  VI. ]  The  living  tree  had  three  main  laterally  directed 
roots  of  this  sort.  They  were  vertically  flattened  for  about  eight 
inches  and  then  contracted  rather  abruptly  to  two  inches  in  diame- 
ter, tapering  gradually  from  this  point  to  their  extremities.  After 
leaving  the  trunk  they  rose  toward  the  surface  and  lay  for  a  dis- 
tance of  nineteen  feet  out  from  the  tree  among  the  roots  of  clover 
and  grasses.  Besides  their  main  roots  were  a  few  whip-like  roots 
of  the  same  sort,  lying  even  nearer  the  surface  than  the  large  ones. 


WHAT  is  THE  MATTER  WITH  THE  ELMS?  9 

The  only  other  roots  present  were  eight  small  brace  roots  from 
one-half  to  one  inch  in  diameter,  which  extended  downward  into 
the  soil  at  an  angle  of  about  45  degrees.  So  long  as  they  were  un- 
cut the  tree  stood  firmly  in  place,  though  the  soil  was  removed  for 
a  depth  of  several  feet.  The  long  lateral  roots  were  all  cut  and 
still  the  tree  could  not  be  moved  until  these  little  roots  were  sev- 
ered. The  second  tree  had  more  of  the  lateral  roots,  but  they  arose 
and  extended  outward  like  those  of  the  first.  The  brace  roots  were 
of  the  same  character  and  of  about  the  same  number. 

"Trees  with  such  a  root  system  are  adapted  to  alluvial  soils, 
rich  and  easily  penetrated.  A  certain  amount  of  moisture  is  also 
essential  to  them.  Under  natural  conditions  elms  grow  among 
other  plants,  interspersed  with  other  trees.  The  ground,  besides 
being  rich  and  from  situation  moist,  is  protected  during  winter  by 
a  mulch  of  dead  leaves  and  in  summer  by  shade  and  perhaps  a 
tangle  of  undergrowth.  Soil  so  protected  does  not  give  up  its 
moisture  quickly.  But  let  such  trees  be  exposed  to  the  heat  of  the 
summer  sun  by  cutting  away  all  other  trees,  or  by  keeping  the 
grass  browsed  or  mowed  closely  over  their  long  roots,  and  they 
become  enfeebled  in  time  and  ready  to  succumb  when  any  sudden 
and  exceptionally  severe  drought  or  freeze  comes.  Even  if  the 
removal  of  our  forests  had  no  other  effect  than  exposing  the  soil 
to  the  sun  it  is  probable  that  such  isolated  trees  would  suffer  in 
time.  But  removal  of  vast  tracts  of  forest,  coupled  with  tillage 
and  other  processes  involved  in  peopling  a  country,  is  known  to 
encourage  drought  in  other  ways :  By  favoring  a  rapid  escape  of 
rainfall  by  surface  drainage,  a  process  that  is  accelerated  artificially 
by  ditching,  tile  draining,  and  the  like,  eventually  leading  to  con- 
stant late  summer  droughts  from  which  not  only  trees  but  all  other 
plants  suffer.  A  tree  with  an  extensive  root  system  may  not  show 
the  effect  in  one  year,  or  in  two,  but  in  the  course  of  many  years 
the  available  food  supply  becomes  exhausted,  having  been  in  part 
leached  away  by  the  running  waters,  and  no  fresh  humus  being 
supplied,  the  inevitable  result  is  exhaustion  for  lack  of  both  food 
and  moisture.  The  effect  shows  first  by  the  death  of  tips  of 
branches,  the  tree  not  having  vitality  sufficient  to  keep  up  the  cir- 
culation in  the  extremities,  and  the  tree  becomes  'stag  headed,'  to 
use  an  imported  term. 

"If  one  looks  about  in  Bluegrass  Kentucky  he  will  see  many 
trees  in  this  condition,  oaks,  ash  and  maples.  The  trouble  is  of 
course  more  or  less  serious  according  to  the  exposure  of  the  roots. 

"Not  only  do  trees  fail  to  show  signs  of  suffering  immediately 
after  the  surface  is  cleared,  but  it  is  known  to  experienced  forest- 
ers that  for  a  time  they  grow  more  rapidly  and  appear  to  be  in 


10  BULLETIN  No.  154  [February, 

better  condition.  This  is  explained  as  the  result  of  an  increased 
food  supply,  due  to  the  removal  of  competitors,  to  a  more  rapid 
decomposition  of  humus,  which  results  from  exposure  to  the  air, 
and  to  increased  sunlight.  It  is  only  after  a  considerable  period 
that  the  final  effect  of  deforesting  is  felt  by  the  trees  and  perceived 
by  man.  Such  results  are  not  restricted  to  this  country,  but  are 
known  among  foresters  the  world  over. 

"I  take  it  we  are  now  witnessing  some  of  these  effects  in  Ken- 
tucky, and  that  our  elms  feel  the  change  most  keenly  because  of 
their  manner  of  rooting.  The  debility  brought  about  by  unfavor- 
able conditions  such  as  those  described  is  taken  advantage  of  by 
the  elm  tree  borer*  in  some  cases,  which  completes  the  ruin  by 
girdling  trees  under  the  rough  outer  bark." 

PROSPECTS  OF  CONTINUANCE 

There  is  nothing  more  characteristic  of  unusual  outbreaks  of 
insect  injury  than  their  temporary  character.  Altho  it  seemed  in 
1884  that  the  elms  of  central  Illinois  towns  would  probably  all  be 
gone  in  a  few  years,  their  epidemic  disease  diminished  in  the  fol- 
lowing years  almost  as  rapidly  as  it  had  developed.  Single  cases 
were  still  to  be  found  ten  years  later,  but  many  of  the  affected  trees 
recovered,  and  there  has  been,  until  lately,  only  an  occasional  trace 
of  this  special  trouble  in  that  part  of  the  state  since  1895. 

In  Kentucky  also  the  heavy  loss  of  elms  which  was  the  occasion 
of  the  bulletin  of  Professor  Carman  quoted  above  has  now  prac- 
tically ceased;  and  in  a  letter  dated  June  3,  1910,  he  says:  "Our 
elms  have  largely  recovered  since  my  bulletin  was  written,  altho 
a  good  many  of  them  were  lost  during  the  excessively  dry  period 
of  which  the  bulletin  treated.  During  the  past  three  years  we  have 
had  more  rainfall  than  we  wanted  at  times,  and  the  trees  every- 
where are  looking  fine." 

The  case  is  therefore  not  as  hopeless  as  it  now  looks,  for  the 
elms  of  southern  Illinois  towns,  altho  the  past  summer  has  been  a 
peculiarly  trying  one.  If  the  weather  of  the  next  years  is  normally 
moist,  it  is  quite  possible  that  many  of  the  injured  trees  favorably 
situated  may  recover,  and  that  the  general  condition  of  the  elms 
thruout  the  country  will  become  greatly  improved.  If,  however, 
weather  conditions  should  continue  unfavorable,  the  injury  will  go 
on  in  all  probability  to  still  greater  extremes.  In  any  event  meth- 
ods of  prevention  and  remedy  are  important  to  all  who  value  their 


"*Two  other  beetles  belonging  to  the  same  family  as  the  elm  borer,  were 
reared  by  me  [Garman]  some  years  ago  from  diseased  elms.  They  are 
Dularius  brev ilineus  and  Xylotrechus  colonus." 


WHAT  is  THE  MATTER  WITH  THE  ELMS?  11 

trees,  especially  as  the  causes  of  the  present  trouble  are  to  be  found 
in  great  measure  in  previous  mismanagement. 

REMEDY  AND  PREVENTION 

The  truth  is  that  our  shade  trees  have  commonly  been  treated 
as  if,  unlike  any  other  crop  we  raise,  they  needed  neither  care  nor 
cultivation,  but  once  set  out  would  take  care  of  themselves  forever. 
This  is  not  true,  as  we  now  know,  for  even  forest  trees  growing 
under  native  conditions ;  and  it  is  peculiarly  false  for  trees  planted 
in  more  or  less  unnatural  situations,  and  for  those  whose  original 
surroundings  have  been  changed  materially  for  the  worse.  Here 
especially  the  elm  must  be  watched  and  cared  for;  fed,  watered, 
and  protected ;  relieved  from  the  attacks  of  its  insect  enemies,  and 
surgically  treated  to  heal  the  wounds  they  have  made.  The  amount 
of  attention  it  will  require  will  vary,  of  course,  with  its  situation, 
including  the  condition  of  other  trees  on  adjacent  premises.  In- 
deed, no  really  satisfactory  program  of  protection  and  maintenance 
can  be  worked  out  except  by  cooperation  of  all  concerned.  A  single 
badly  infested  tree,  kept  because  of  the  indifference  of  its  owner, 
may  be  a  constant  menace  to  all  the  other  elms  in  its  neighborhood, 
however  intelligently  they  may  be  cared  for. 

The  main  effort  must  be  at  first  to  supply  to  endangered  trees, 
and  especially  to  those  beginning  to  fail,  the  water  and  plant  food, 
a  lack  of  which  is  the  most  serious  feature  of  their  situation.  Well- 
rotted  stable  manure  spread  generously  around  the  tree  as  far  as 
its  roots  extend,  with  an  occasional  free  watering  of  the  soil  during 
periods  of  severe  drouth,  will  meet  these  requirements.  If  the 
manure  can  be  left  during  dry  periods  as  a  mulch,  the  chances  of 
the  tree  will  be  greatly  improved.  The  watering  must  not  be  a 
mere  surface  sprinkling,  but  should  soak  the  ground  to  a  depth  of 
several  inches. 

When  it  is  necessary  to  trim  a  tree,  superfluous  branches  should 
be  cut  or  sawed  smoothly  away  at  their  very  beginning.  To  cut  or 
hack  them  off  irregularly,  leaving  projecting  stubs  to  dry  up  and 
decay,  is  simply  to  invite  the  attacks  of  borers  by  offering  them  a 
favorable  place  of  deposit  for  their  eggs.  For  the  same  reason 
dead,  dying,  or  badly  injured  limbs  should  be  promptly  cut  out  and 
burned. 

This  is  as  good  a  place  as  any  to  enter  an  emphatic  protest 
against  the  practice  of  topping  or  pollarding  trees  like  the  elm,  not 
only  because  their  natural  beauty  is  forever  destroyed  by  the  proc- 
ess, but  also  because  the  tree  is  peculiarly  exposed  by  it  to  fatal 
infestation  by  its  most  destructive  insect  enemies. 


12  BULLETIN  No.  154  [February, 

Further  protection  against  borers  may  be  given  by  a  thick  coat 
of  paint  applied  to  cut  surfaces  and  repeated  after  the  first  coat  is 
dry.  Any  paint  will  do  which  is  made  of  linseed  oil  and  lead. 
Ordinary  ready-made  paints  are  nearly  useless  for  this  purpose, 
since  they  are  likely  to  crack  and  scale  off.  As  a  general  preventive 
of  borer  infestation,  the  trunk  of  the  tree  and  the  larger  branches 
may  be  painted  with  a  mixture  intended  to  prevent  the  laying  of 
the  eggs.  Some  of  the  mixtures  recommended  are  prepared  as  fol- 
lows :  To  a  gallon  of  soft  soap  add  half  a  gallon  of  hot  water  and 
a  pint  of  crude  carbolic  acid,  or  a  half  pint  of  the  refined  acid, 
stirring  the  latter  thoroly  in  and  leaving  the  mixture  over  night. 
Then  dilute  with  eight  gallons  of  water  and  apply  with  a  white- 
wash brush.  Or,  to  a  saturated  solution  of  washing  soda  add  soft 
soap  to  make  a  thick  paint,  and  stir  in  a  pint  of  crude  carbolic  acid 
and  half  a  pound  of  Paris  green  to  each  ten  gallons  of  the  wash. 
Or,  in  six  gallons  of  a  saturated  solution  of  washing  soda  dissolve 
a  gallon  of  soft  soap,  add  a  pint  of  carbolic  acid,  mixing  well,  slake 
enough  lime  in  four  gallons  of  water  to  form  a  thick  whitewash 
as  it  is  added  to  the  foregoing,  and  finally  stir  in  thoroly  a  half 
pound  of  Paris  green.  One  or  the  other  of  these  substances  should 
be  applied,  as  frequently  as  may  be  necessary  to  keep  the  bark 
moist,  from  the  middle  of  May  to  the  end  of  July. 

THE  INSECTS  CHIEFLY  CONCERNED 

Of  all  the  many  insect  eliemies  to  the  elm  in  Illinois,  much  the 
most  destructive  is  the  "round-headed"  borer  commonly  known  to 
entomologists  as  the  elm-borer  (Saperda  tridentatd).  Even  more 
abundant  than  this,  but  less  injurious,  is  a  much  smaller  burrow- 
ing grub,  the  larva  of  the  reddish  elm  snout-beetle  (Magdalis  armi- 
collis}.  It  is  the  common  elm-borer,  working  in  tlie  bark  and  the 
sap-wood  of  the  elm,  to  which  the  present  condition  of  our  dead 
or  dying  trees  is  most  commonly  attributed  by  those  searching  for 
a  cause.  It  is  a  common  belief,  however — difficult  to  prove,  it  is 
true,  and  at  best  a  matter  of  intelligent  opinion — that  this  beetle 
attacks  by  preference  trees  already  suffering  from  some  disease  or 
other  crippling  condition.  It  would  be  easier  to  make  sure  that 
this  is  true  if  it  were  not  for  the  fact  that  it  is  difficult  to  detect 
the  beginnings  of  injury  by  this  insect.  Often  the  first  notice  one 
has  of  its  presence  is  a  general  failure  of  the  tree,  due  to  an  in- 
festation already  extensive  and  long  continued;  and  whether  this 
failure  began  before  the  borer  injury  or  was  caused  by  it,  one  can 
not  positively  tell.  This  is,  indeed,  a  matter  of  little  practical  im- 
portance, since  one  must  proceed  in  the  same  way  whichever  view 
he  takes.  That  the  elm  snout-beetle  infests  dying  trees  in  prefer- 


1912} 


WHAT  is  THE  MATTER  WITH  THE  ELMS? 


13 


ence  to  healthy  ones,  can  not  be  doubted,  for  the  larva  is  abundant 
in  the  dead  wood  of  a  dying  tree  but  occurs  very  rarely  in  the  liv- 
ing tissue. 

THE  ELM-BORER 
Saperda  tridentata  Oliv. 

In  the  larval  or  boring  stage  this  elm  insect  may  be  readily 
recognized  by  those  at  all  familiar  with  the  round-headed  borer  of 
the  apple,  because  of  the  close  resemblance  of  the  two.  They  be- 
long, in  fact,  to  nearly  related  species  of  the  same  genus. 


Fig-.  1.  The  Elm-borer,  Saperda 
tridentata,  larva.  (Enlarged  S  dia- 
meters.) 

The  full-grown  boring  larva  (Fig.  i)  is  a  footless  grub  a  little 
over  an  inch  in  length,  white  .or  yellowish  white,  thickest  in  front, 
and  with  the  head  only  about  half  as  wide  as  the  first  segment  be- 
hind it.  The  body  is  slightly  flattened  from  above  downward,  with 
a  rather  pronounced  fold  along  the  sides.  The  first  segment  is 


14 


BULLETIN  No.  154 


[February, 


about  twice  as  broad  as  long,  and  has  upon  its  upper  surface  a 
pale,  horny,  oblong,  transverse  shield  or  cover  about  two  thirds  as 
long  as  wide.  This  is  roughened  on  the  posterior  half,  but  is  else- 
where smooth.  On  the  upper  side  of  each  remaining  segment  is 
an  ovate,  roughened,  transverse  area,  slightly  convex  in  front  and 
slightly  concave  behind. 

The  pupa,  which  may  be  found  in  a  cell  beneath  the  bark,  is 
yellowish  white,  about  half  an  inch  long,  and  with  slender  an- 
tennae lying  along  each  side  and  bent  forward  over  the  breast. 


Fitf.  2.  Adult,  or  beetle,  of  the  tlni-borer, 
Saperda  tridentata.    (Enlarged  4  diameters.) 

The  parent  beetle  (Fig.  2)  is  of  a  grayish  color,  due  to  a  very 
fine  gray  down  which  densely  clothes  the  surface.  On  each  side 
of  the  thorax  and  on  each  wing  cover  is  a  submarginal  reddish  or 
yellowish  stripe,  and  from  each  of  these  stripes  three  oblique  bands 
project  inward  and  backward  to  a  variable  distance  in  different 
specimens.  Sometimes  they  extend  across  the  wing  cover  to  meet 
the  corresponding  bands  on  the  opposite  side,  and  sometimes  they 
are  short  oblique  branches  only.  There  are  often  two  black  spots 
on  each  side  of  the  thorax,  and  three  on  each  wing  cover. 

Strangely  enough,  the  life  history  of  this  abundant  insect  has 
never  been  worked  out,  but  there  is  good  reason  to  suppose  that 
it  extends  over  two  or  three  years.  Indeed,  in  the  northern  part 
of  the  area  of  distribution  of  the  species,  as  many  as  three  distin- 


1912} 


WHAT  is  THE  MATTER  WITH  THE  ELMS? 


15 


guishable  sizes  of  the  larvae  may  be  found  at  one  time  in  the  mines 
under  the  bark,  each  apparently  representing  a  different  generation. 
The  eggs  are  deposited  in  June  and  July  and  possibly  later,  as  the 
beetles  are  abroad  until  towards  the  middle  of  August.  The  young 
grub,  after  hatching,  works  its  way  under  the  bark,  making  a  ser- 
pentine burrow  as  it  feeds,  which  increases  in  size  with  the  growth 
of  the  larva  and  in  course  of  time  may  completely  girdle  the  tree. 
When  the  larvae  are  full-grown  they  change  to  the  pupa  in  the 
early  part  of  the  year,  and  the  beetles  begin  to  appear  in  May.* 

This  species  has  been  recorded  from  Vermont,  Canada,  and 
Wisconsin,  to  Pennsylvania,  Kentucky,  Illinois,  and  Iowa.  It 
seems  to  have  a  general  distribution  thruout  the  northeastern 
United  States. 

THE  REDDISH  EI/M  SNOUT-BEETLE 
Magdalis  armicollis  Say 

A  small  boring  grub  about  a  quarter  of  an  inch  long  or  less, 
frequently  associated  with  the  round-headed  borer  of  the  elm  often 
occurs  in  immense  numbers  in  the  recently  dead  wood  of  the  elm, 


Fig-.  3.     Elm  Snout-beetle,  Magdalis  armicollis:  larva,  pupa,  and  adult  beetle. 
(Enlarged  8  diameters.) 

and  sometimes  extends  its  burrows  into  the  still  living  tissue  ad- 
jacent. It  is  a  small,  plump,  entirely  footless,  whitish  grub,  lying 
partly  curled  up  in  the  usual  grub  fashion  when  at  rest.  The  head 
is  small,  but  the  three  segments  back  of  the  head  .are  noticeably 

*My  office  collections  of  the  beetles  range  from  May  19  to  August  8. 


16 


BULLETIN  No.  154 


[February, 


swollen  and  about  one  twelfth  of  an  inch  thick.  The  remainder  of 
the  body  is  more  slender,  slightly  tapering  to  the  smoothly  rounded 
posterior  end.  The  head  is  pale  brown,  and  the  mandibles  and  the 
narrow  front  border  of  the  clypeus  are  dark,  in  decided  contrast 
with  the  labrum,  which  is  whitish.  The  first  segment  back  of  the 
head  is  faintly  brownish,  shining  except  for  a  dull  pubescent  ridge 
along  the  hind  border.  The  remaining  segments,  except  those  near 
the  posterior  end,  which  are  smoother,  bear  two  such  dull  ridges. 
On  the  abdominal  segments  these  ridges  extend  to  the  spiracles  on 
each  side,  and  behind  them  is  an  additional  shorter  ridge  of  similar 
appearance.  The  folds  beneath  the  head  are  also  dull  pubescent. 


Fig.  4.    Elm  twig  with  bark    cut  away  to  show  burrow  of 
Magdalis  armicollis.    (Enlarged  3  diameters.) 

The  beetles,  which  develop  beneath  the  bark  and  escape  from  it 
by  eating  small  round  holes  to  the  surface,  are  from  an  eighth  to 
a  quarter  of  an  inch  in  length,  the  sexes  differing  to  such  an  ex- 
tent that  they  were  originally  described  as  separate  species.  The 
male  is,  in  fact,  decidedly  smaller  than  the  female,  darker  beneath ., 
and  with  a  much  more  marked  contrast  in  color  between  the  wing 
covers  and  the  thorax.  The  wing  covers  are  yellowish,  or  pale 
reddish  brown,  and  are  each  marked  with  nine  deep  longitudinal, 
coarsely  punctured,  grooves.  The  thorax  and  the  head  are  decid- 
edly darker,  especially  in  the  male,  in  which  they  are  frequently 
black.  The  thorax  is  narrower  than  the  wing  covers,  broadly 
rounded  laterally  and  very  densely  punctured  above  and  on  the 
sides,  with  a  more  or  less  evident  smooth  median  raised  line.  The 
body  beneath  is  pale  reddish  brown  in  the  female,  and  black  in  the 
male.  The  projecting,  slightly  curved  snout  is  about  as  long  as 
the  thorax,  and  bears  the  antennae  near  its  tip. 

The  larvae  pupate  in  spring  within  the  tree,  and  the  beetles 
emerge  in  about  three  weeks,  pairing  and  laying  their  eggs  in  May 
and  June. 


1912} 


WHAT  is  THE  MATTER  WITH  THE  ELMS? 


17 


PL,ATE  I. 

EI,M-TREE  —  DIED  DURING  SUMMER  OK  1911.     NORMAL  SCHOOL  CAMPUS, 
CARBONDAI^E,  SEPTEMBER  20,  1911. 


18 


BULLETIN  No.  154 


[February, 


PLyATE  II. 

EI.M-TREE — DIED  DURING  SUMMER  OF  1911.    NORMAI,  AVENUE,  CARBONDAI^E, 

SEPTEMBER  20,  1911. 


I9I2] 


WHAT  is  THE  MATTER  WITH  THE  ELMS? 


PLATE  III. 

DIED  DURING  SUMMER  OF   1911.     NORMAI,  A  VENUE,  CARBONDAI<E, 
SEPTEMBER  20,  1911. 


20 


BULLETIN  No.  154 


[February, 


PL,ATE  IV. 

A  DISEASED  EI,M  GROWING  ON  THE  GROUNDS  OK   THE    KENTUCKY    STATE    UNI- 
VERSITY.    PHOTOGRAPHED  AUGUST  28,  1899.     (FROM  PROK.  H.  GARMAN.) 


1912} 


WHAT  is  THE  MATTER  WITH  ELMS? 


21 


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